Generally, in a solar power generation system, an inverter is used to connect to an electric power system. The inverter converts direct current power generated by the solar cell into alternating current power synchronous with the electric power system, and supplies the alternating current power to the electric power system.
For example, to prevent the reverse flow of the output current, a system-connected device has been discussed in which the system voltage is sensed, and a voltage step-up circuit is controlled to provide an optimal stepped-up voltage that is higher than the sensed system voltage by the amount of a predetermined voltage value (e.g., referring to Patent Document 1).
However, when performing maximum power point tracking (MPPT, maximum power point tracking) of the inverter to cause the electrical power output from the solar cell to be a maximum, the lower limit of the direct current voltage is preset. Therefore, when operating, even if the inverter is in a state in which the inverter is operatable at a direct current voltage lower than the lower limit, the control device of the inverter cannot control at a direct current voltage lower than the preset lower limit.